The present invention relates to charged particle lithography method and system for writing a design pattern formed on a mask onto a substrate by using charged particles in fabrication of a semiconductor device, a liquid crystal display device or a thin film magnetic head device.
In photolithography now used in fabrication of a semiconductor device and the like, a KrF excimer laser beam with a wavelength of 248 nm is used as a light source. Furthermore, lithography using an ArF excimer laser beam with a wavelength of 193 nm is planned to be adopted as the next generation photolithography. However, for further refinement of devices, there is a limit in the resolution between design patterns attained by the photolithography.
Therefore, various types of lithography techniques have been proposed, among which lithography technique using charged particles, such as ions and electrons, particularly an electron beam, is regarded promising. The electron beam lithography method is divided into a method using a mask bearing a design pattern and a method not using a mask.
Now, a conventional electron beam lithography method using a mask will be roughly described with reference to drawings. FIG. 19 is a diagram for illustrating the conventional electron beam lithography method in which an electron beam 103 is scanned across a mask 101 bearing a desired circuit pattern 102. As is shown in FIG. 19, an electron beam emitted from an electron gun is allowed to pass through a shaping aperture (not shown) to be shaped into an electron beam with a section of, for example, approximately 1 mmxc3x971 mm, and the mask 101 bearing the desired circuit pattern 102 is exposed to the shaped electron beam. The electron beam having passed through the mask 101 is reduced by an electron lens, and exposes a substrate (not shown) coated with a resist. In general, the circuit pattern 102 is sufficiently larger than the dimension of the shaping aperture. Accordingly, as is shown in FIG. 19, by repeating scanning of the circuit pattern 102 from one end to the other end thereof with the mask 101 continuously moved by using the effective width of the shaping aperture as a pitch P, the entire circuit pattern 102 is exposed zonally to the electron beam 103.
The conventional electron beam lithography method, however, has the following problem: As is shown in FIG. 20, during the repeated scanning of the electron beam 103, there arises a connection error between partial exposure areas 104A, 104B and 104C, each of which corresponds to an area exposed in one of the repeated scanning. In the case shown in FIG. 20, the first partial exposure area 104A and the second partial exposure area 104B are away from each other and the second exposure area 104B and the third exposure area 104C overlap each other. This problem occurs depending upon alignment accuracy of a stage for supporting the substrate or the mask and stability of the used electron beam.
The connection error caused between the partial exposure areas leads to the following problems in wiring a pattern across the connection between the partial exposure areas: When the partial exposure areas are away from each other, disconnection is caused as is shown in FIG. 21(a), and when the distance therebetween is small, a line width failure where the line width is locally reduced is caused as is shown in FIG. 21(b), and hence there is fear of disconnection. Furthermore, when the partial exposure areas overlap each other, a line width failure where the line width is locally increased is caused as is shown in FIG. 21(c). In any case, a failure can be caused in the resultant circuit pattern.
In view of the aforementioned conventional problems, an object of the invention is preventing fatal deformation of a circuit pattern without lowering throughput even when there arises a connection error between partial exposure areas.
In order to achieve the object, according to the invention, respective exposure areas are exposed to be partially overlapped in repeating partial transfer of a design pattern formed on a mask, so that an exposure dose in a double exposure portion and an exposure dose in a normal exposure portion that is not doubly exposed can be equal to each other.
Specifically, the charged particle lithography method of this invention comprises a beam shaping step of shaping an output beam emitted from a charged particle producing source into a predetermined shape; and a design pattern transferring step of transferring a design pattern formed on a mask onto a substrate by repeating partial transfer for transferring a part of the design pattern onto the substrate by allowing the shaped beam to transmit the part of the design pattern and exposing a part of the substrate to the transmitted beam, wherein the design pattern transferring step includes, in conducting the partial transfer, a step of forming a double exposure portion that is doubly exposed in an exposure area on the substrate exposed to the beam, and exposing the exposure area so that an exposure dose in the double exposure portion and an exposure dose in a non-double exposure portion that is not doubly exposed are substantially the same.
In the charged particle lithography method of this invention, a double exposure portion that is doubly exposed in repeated partial transfer is formed in an exposure area on the substrate. Therefore, a margin for moving the beam can be so large that exposure areas are difficult to be away from each other. Also, the exposure is conducted so as to attain substantially the same exposure dose in the double exposure portion and the non-double exposure portion that is not doubly exposed in the exposure area. Therefore, a line width failure can be prevented from being caused in a design pattern in the double exposure portion. Furthermore, even when the exposure areas are away from each other, the exposure dose is prevented from being 0, and even when the exposure areas are largely overlapped, the exposure dose is not doubled. Accordingly, disconnection and deformation of a resist pattern derived from a connection error occurring in repeating the partial exposure can be prevented, resulting in improving the performance and the yield of semiconductor devices.
In the charged particle lithography method, the beam shaping step preferably includes a step of shaping the output beam so that an exposure dose of the output beam at a center of a line extending between an end of the double exposure portion closer to the non-double exposure portion and the other end of the double exposure portion farther from the non-double exposure portion is approximately a half of an exposure dose in the non-double exposure portion, and the design pattern transferring step preferably includes a step of scanning the shaped beam across the mask and the substrate zonally. In this manner, even when the exposure is conducted by the scanning method, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion.
In the charged particle lithography method, the beam shaping step preferably includes a step of continuously changing the output beam so that an exposure dose of the output beam in the double exposure portion is 0 at an end thereof farther from the non-double exposure portion and is a predetermined dose at the other end closer to the non-double exposure portion, and the design pattern transferring step preferably includes a step of scanning the shaped beam across the mask and the substrate zonally. In this manner, even when the exposure is conducted by the scanning method, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion.
In the charged particle lithography method, the beam shaping step preferably includes a step of shaping the output beam so that an exposure dose of the output beam in the double exposure portion is approximately a half of an exposure dose in the non-double exposure portion, and the design pattern transferring step preferably includes a step of exposing the mask and the part of the substrate to the shaped beam with the shaped beam stopped, and moving the shaped beam so as to doubly expose an end portion of the exposure area toward a direction of moving the shaped beam. In this manner, even when the exposure is conducted by a step-and-repeat exposure method, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion.
In adopting the step-and-repeat exposure method, the beam shaping step preferably includes a step of shaping the output beam so that an exposure dose of the output beam in the double exposure portion at each of four corners in the exposure area is approximately xc2xc of an exposure dose in the non-double exposure portion. In this manner, even when the exposure is conducted by the step-and-repeat exposure method in which the double exposure portions at four corners of the exposure area are exposed four times, the exposure dose in each double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion.
In the charged particle lithography method, the double exposure portion preferably has a width smaller than approximately one-hundredth of a distance to move the exposure area in repeating the partial transfer. In this manner, the throughput can be prevented from lowering.
In the charged particle lithography method, the double exposure portion preferably has a width smaller than approximately one-hundredth of a width of the exposure area. In this manner, the throughput can be prevented from lowering.
The first charged particle lithography system of this invention for writing a design pattern formed on a mask onto a substrate by repeating exposure of a part of the design pattern to a beam of charged particles with the part of the design pattern partially overlapped in each exposure, comprises charged particle producing means for emitting the beam to the substrate; substrate supporting means for supporting the substrate; mask supporting means for supporting the mask between the charged particle producing means and the substrate; a shaping aperture for shaping the beam into a predetermined shape disposed between the charged particle producing means and the mask supported by the mask supporting means; and moving means for moving the mask supporting means and the substrate supporting means relatively to the charged particle producing means, wherein the shaping aperture has an aperture pattern for attaining substantially the same exposure dose in a double exposure portion that is doubly exposed and in a non-double exposure portion that is not doubly exposed, the double exposure portion and the non-double exposure portion being formed in an exposure area on the substrate exposed to the beam having passed through the mask.
In the first charged particle lithography system, a double exposure portion that is doubly exposed is formed in an exposure area on the substrate exposed to the beam having passed through the mask. Therefore, a margin for moving the beam is so large that the exposure areas are difficult to be away from each other. Furthermore, since the shaping aperture has the aperture pattern for attaining substantially the same exposure dose in the double exposure portion and the non-double exposure portion that is not doubly exposed in the exposure area. Therefore, a line width failure can be prevented from being caused in a design pattern in the double exposure portion. In addition, even when the exposure areas are away from each other, the exposure dose is prevented from being 0, and even when the exposure areas are largely overlapped each other, the exposure dose is not doubled. Accordingly, disconnection and deformation of a resist pattern derived from a connection error occurring in repeating the partial transfer can be prevented, resulting in improving the performance and the yield of semiconductor devices.
In the first charged particle lithography system, an area of the aperture pattern corresponding to the double exposure portion preferably has an aperture ratio of substantially 50% and an area of the aperture pattern corresponding to the non-double exposure portion has an aperture ratio of substantially 100%. In this manner, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion in the exposure area.
In this case, the aperture pattern is preferably in the shape of a parallelogram having, as opposing oblique sides, sides of the area of the aperture pattern corresponding to the double exposure portion. Thus, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion in the exposure area.
Alternatively, the aperture pattern is preferably in the shape of a trapezoid having, as opposing oblique sides, sides of the area of the aperture pattern corresponding to the double exposure portion. Thus, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion in the exposure area.
In the first charged particle lithography system, the area of the aperture pattern corresponding to the double exposure portion preferably has transmittance of substantially 50% and the area of the aperture pattern corresponding to the non-double exposure portion preferably has transmittance of substantially 100%. In this manner, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion in the exposure area.
The second charged particle lithography system of this invention for writing a design pattern formed on a mask onto a substrate by repeating exposure of a part of the design pattern to a beam of charged particles with the part of the design pattern partially overlapped in each exposure, comprises charged particle producing means for emitting the beam to the substrate; substrate supporting means for supporting the substrate; mask supporting means for supporting the mask between the charged particle producing means and the substrate; and moving means for moving the mask supporting means and the substrate supporting means relatively to the charged particle producing means, wherein the charged particle producing means includes plural charged particle sources arranged for attaining substantially the same exposure dose in a double exposure portion that is doubly exposed and in a non-double exposure portion that is not doubly exposed, the double exposure portion and the non-double exposure portion being formed in an exposure area on the substrate exposed to the beam having passed through the mask.
In the second charged particle lithography system, a double exposure portion that is doubly exposed is formed in an exposure area on the substrate exposed to the beam having passed through the mask. Therefore, a margin for moving the beam is so large that the exposure areas are difficult to be away from each other. Furthermore, since the charged particle producing means includes the plural charged particle sources arranged so that the exposure dose can be substantially the same in the double exposure portion and the non-double exposure portion that is not doubly exposed in the exposure area. Therefore, a line width failure can be prevented from being caused in a design pattern in the double exposure portion. In addition, even when the exposure areas are away from each other, the exposure dose is prevented from being 0, and even when the exposure areas are largely overlapped each other, the exposure dose is not doubled. Accordingly, disconnection and deformation of a resist pattern derived from a connection error occurring in repeating the partial transfer can be prevented, resulting in improving the performance and the yield of semiconductor devices.
In the second charged particle lithography system, charged particle sources arranged in an area corresponding to the double exposure portion in the charged particle producing means preferably have a charged particle emission energy of substantially 50% of a charged particle emission energy of charged particle sources arranged in an area corresponding to the non-double exposure portion. In this manner, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion in the exposure area.
In the second charged particle lithography system, the number of charged particle sources arranged in a direction of moving the beam in an area corresponding to the double exposure portion in the charged particle producing means is preferably substantially a half of the number of charged particle sources arranged in an area corresponding to the non-double exposure portion. In this manner, the exposure dose in the double exposure portion can be substantially the same as the exposure dose in the non-double exposure portion in the exposure area.
In the first or second charged particle lithography system, the mask supporting means is preferably a mask stage and the substrate supporting means is preferably a substrate stage, and the moving means preferably moves the mask stage and the substrate stage in synchronization with each other. In this manner, for moving the mask and the substrate relatively to the charged particle beam for exposure, the movement is made easier and the range of the movement is wider by moving the stages than by moving the charged particle beam. Accordingly, the design pattern on the mask can be definitely transferred onto the substrate.